Diorganomagnesium compounds are well known for their usefulness in a wide variety of chemical reactions. As reagents, these compounds can be used for the alkylation of ketones and the alkylation of metal halides or oxides to the corresponding metal alkyls. As catalysts, diorganomagnesium compounds are useful in the dimerization and polymerization of olefins, (British Pat. No. 1,251,177), the polymerization of epoxides, (U.S. Pat. No. 3,444,102), and the preparation of telomers, (U.S. Pat. No. 3,742,077). While they perform many of the same types of functions performed by Grignard reagents, diorganomagnesium compounds, owing to differences in electronic and steric factors, are more reactive than Grignard reagents toward certain types of compounds. In general, see also U.S. Pat. Nos. 3,646,231 and 3,822,219.
The utility of diorganomagnesium compounds is lessened by the fact that many are either solids or highly viscous liquids. This problem is generally overcome either by dissolving the compound in an inert hydrocarbon solvent or by solvating the compound. All are unstable upon exposure to moisture and air and require handling under an inert atmosphere. Some diorganomagnesium compounds, with straight chain lower alkyl groups of up to four carbon atoms, have a relatively low solubility by themselves in hydrocarbon solvents and thus require solubilizing agents which will form a soluble complex to achieve useful concentrations. Examples of such solubilizing agents are alkyllithium compounds (U.S. Pat. No. 3,742,077), dialkyl zinc compounds (U.S. Pat. No. 3,444,102), alkali metal hydrides (U.S. Pat. No. 3,655,790), and organoaluminum compounds (U.S. Pat. Nos. 3,143,577, 3,737,393 and 3,028,319). Certain combinations of dialkylmagnesium compounds are quite soluble in hydrocarbon solvents. The latter are seen in the Journal of Organometallic Chemistry, 8, 542 (1967) (methyl isobutylmagnesium) and in U.S. Pat. Nos. 4,069,267 (C.sub.1 to C.sub.4 di-n-alkylmagnesium and C.sub.6 to C.sub.18 dialkylmagnesium), 4,127,507 (di-n-butylmagnesium and di-ethylmagnesium), 4,207,207 (dimethylmagnesium and di-n-propylmagnesium) and 4,222,969 (dimethylmagnesium and di-nbutyl magnesium). All of these processes are relatively expensive.
Solvation involves the use of an ether or other organic Lewis base molecule to associate directly with the magnesium atom, thus yielding a hydrocarbon soluble complex. The solvated form is undesirable however, since solvation seriously inhibits the effectiveness of the compound, for some uses, particularly when the compound is used as a component of a Ziegler-type polyethylene catalyst. The use of diethylether is particularly undesirable because it has a low boiling point, is flammable, and its vapors are explosive when mixed with air. It introduces soluble RMgX according to the Schlenk equilibrium.
Even R.sub.2 Mg often gives hydrocarbon solutions of relatively high viscosity which are difficult to handle and transfer. The use of chloroaryl solvents to form low viscosity solutions of the otherwise insoluble compounds, as described in U.S. Pat. No. 3,264,360 only partially solves this problem.
In addition, the relatively low solubility of the lower alkyl magnesium compounds makes preparation of them in a form free of undesirable co-product magnesium halides difficult. See in particular the direct reaction of magnesium metal with an organic halide as is disclosed in Glaze and Selman, Journal of Organometallic Chemistry, Vol. 5. p. 477 (1967), and W. N. Smith, Journal of Organometallic Chemistry, Vol. 64, p. 25 (1974). These articles deal with the preparation of diorganomagnesium compounds with straight chain alkyl groups of five carbon atoms and higher. Such compounds are soluble in hydrocarbon solvents and thus readily separable from the concurrently produced magnesium halide and unreacted magnesium. When lower straight chain alkyls are used in this process, the desired diorganomagnesium compound is formed but is largely insoluble and exists as a slurry in the solvent together with the magnesium halide and unreacted magnesium metal. Thus a solubilizing agent is required when this process is used to make lower alkyl diorganomagnesium compounds. The latter are particularly desirable as reagents and catalysts owing to their relatively low cost and high magnesium content on a weight basis.
Other methods of preparation include the mercury-magnesium exchange method, as disclosed in Cowan and Mosher, Journal of Organic Chemistry, Vol. 27, p. 1 (1962), and the dioxanate-precipitation method, as disclosed in Schlenk, Berichte der Deutschen Chemischen Gaesellschaft, Vol. 64, p. 734 (1931). The mercury method where R is alkyl, is limited by the high cost of dialkylmercury compounds and the health hazards involved in their use. The reaction itself is hazardous since it proceeds rapidly and exothermically after an inhibition period.
The dioxanate-precipitation method involves removal of magnesium halide from ether solutions of Grignard reagents by precipitation of a complex which the dioxane forms with the halide. This is a tedious process and results in an etherated dialkylmagnesium complex from which the ether must be removed prior to use as a catalyst component in Ziegler-type polymerizations.
U.S. Pat. No. 3,646,231 discloses that dialkylmagnesiums can also be prepared from alkyllithiums and magnesium halides by precipitation of lithium halide.
Such a process is unsuitable for straight-chain lower alkyl diorganomagnesiums which are insoluble in hydrocarbon solvents, since separation from co-product lithium chloride will be impossible. The use of basic solvents renders separation possible but requires subsequent desolvation.
Blitzer et al U.S. Pat. No. 2,959,625 which issued on Nov. 8, 1960 describes the manufacture of alkyl magnesium compounds by reacting magnesium hydride in a reaction medium in the presence of a catalyst, with an olefin hydrocarbon such as ethylene or propylene at a temperature of about 50.degree. to 200.degree. C. and elevated pressure up to about 700 atmospheres. The reaction medium may be an ether having the basicity of that of di-n-butyl ether or below or an aromatic hydrocarbon such as benzene, toluene and xylene. An inert or inactive diluent liquid such as hexane or heptane may additionally be present. A mixed dialkylmagnesium product, namely ethylpropyl magnesium is disclosed.
Podall U.S. Pat. No. 2,985,692 which issued on May 23, 1961 is similar to the Blitzer et al patent, but includes a sulfur compound such as a thioether, a sulfoxide or a sulfone in the reaction medium. A mixed dialkylmagnesium product, namely ethylisopropyl magnesium is disclosed.
Sakurai et al U.S. Pat. No. 4,120,883 which issued on Oct. 17, 1978 discloses a method of making a hydrocarbon soluble organoaluminum magnesium alkoxyalkyl complex from an organomagnesium halide and an organoaluminum halide.
Malpass et al U.S. Pat. No. 4,133,824 which issued on Jan. 9, 1979 describes organomagnesium complexes, namely a complex of magnesium alkyl and an aluminum or other Group II or IIIa metal salt of a fatty acid. The aluminum is at least 10 mole percent of magnesium.
Aishima et al U.S. Pat. No. 4,146,549 which issued Mar. 27, 1979 describes another hydrocarbon-soluble organoaluminummagnesium complex and a process for polymerizing ethylene and another olefin using the complex as a catalyst.
Shepherd U.S. Pat. No. 3,641,186 discloses a process for increasing the molecular weight of a bis-alkenyl magnesium compound by reacting the compound with an olefin in an ether medium.
Shepherd U.S. Pat. No. 3,597,488 discloses a process for increasing the molecular weight of a Grignard reagent by reacting the reagent with an olefin in an ether medium.
Shepherd U.S. Pat. No. 3,670,038 discloses a process for making higher molecular weight dialkylmagnesium compounds from lower molecular weight soluble dialkylmagnesium compounds by reacting the latter with an olefin in the presence of a non-complexing reaction solvent at a pressure of at least about 200 psig and a temperature of about 50.degree. C. to about 250.degree. C.
U.S. Pat. No. 2,475,520 issued to Roedel on July 5, 1949 discloses a process for polymerizing ethylene with Grignard type compounds. In such a process ethylene is polymerized at a temperature between 100.degree. and 400.degree. C. and a pressure between 400 and 1500 atmospheres in the presence of an anhydrous inert solvent medium, such as benzene, isooctane, xylene and diethyl ether and from about 0.005 to 5 percent by weight of a catalyst comprising magnesium metal and alkyl halide capable of yielding an organometallic complex of the formula RMgX where R is an alkyl group and X is a halogen.
Cooper et al U.S. Pat. No. 3,161,689 discloses a process for making Grignard reagents comprising reacting an olefin with an alkyl magnesium halide in a Grignard solvent medium in the presence of a titanium or zirconium catalyst. Such process provides for the use of inexpensive alkyl halides which readily form Grignard reagents to be reacted with long chain or branched chain olefins to form Grignard reagents which heretofore could not easily be obtained.
Shepherd U.S. Pat. No. 3,597,487 describes a process for making mixed dialkylmagnesiums via chain growth wherein ethylene is reacted with a Grignard reagent or diorganomagnesium compound in a non-complexing medium such as a hydrocarbon solvent, at a pressure of at least about 200 psig and a temperature of about 50.degree. to 250.degree. C. Additionally, the patentee discloses that catalytic or small amounts of trialkylaluminum compounds may be used to assist in the chain growth. The hydrocarbyl magnesium compound is prepared by reacting an alkyl halide with magnesium in a suitable solvent. The more readily available and less expensive alkyl halides such as ethyl chloride and propyl chloride may be used to prepare the magnesium compound.
It is an important object of the present invention to provide an improved process for making dialkylmagnesium compounds from readily available and more economical chemical compounds.
Another object of the present invention is to provide a relatively simple and economical process for making mixed dialkylmagnesium compounds and still provide substantial yields.
Still another object of the present invention is to provide a method of making mixtures containing relatively longchain dialkylmagnesium compounds.
Other objects and advantages of the invention will become more readily apparent from a consideration of the description hereinafter.